Sterile alginate-based aqueous composition for medical use and process for the preparation thereof

ABSTRACT

The present invention relates to ready-to-use sterile, alginate-based, aqueous compositions for medical use. More particularly, the invention relates to an aqueous composition for medical use that has been sterilized by heat sterilization and having a viscosity at 25° C. of at least 300 cP) (Helipath® T F spindle, 100 rpm at 25° C.), said composition having a pH in the range of 6.5-7.5; containing 0.5-10 wt. % of an alginate salt; and further containing 10-500 mM of one or more dissolved C 2 -C 7  mono- or dicarboxylates that are optionally substituted with up to 2 hydroxyl groups. 
     The alginate-based composition of the present invention has excellent storage stability and is easy to manufacture. The alginate-based aqueous compositions of the present invention can advantageously be used, for instance, to prevent adhesions between a healing trauma site and adjacent surrounding tissue. These compositions can further be used in implants or in pharmaceutical preparations for oral administration.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to sterile alginate-based aqueouscompositions for medical uses. The alginate-based aqueous compositionsof the present invention can advantageously be used, for instance, toprevent adhesions between a healing trauma site and adjacent surroundingtissue. These compositions can further be used in implants or inpharmaceutical preparations for oral administration.

The invention further relates to a process for the preparation of suchaqueous alginate-based compositions.

BACKGROUND OF THE INVENTION

Adhesions are unwanted tissue growths occurring between layers ofadjacent bodily tissue or between tissues and internal organs. Adhesionsare often formed during the dynamic process of healing of the incisionand tissue trauma after surgery. The initiation of the adhesion beginswith the formation of a fibrin matrix. The ischemic conditions caused bysurgery prevent fibrinolytic activity to dissolve the matrix, and thefibrin persists. Wound repair cells then turn the matrix into anorganized adhesion, often having a vascular supply and neuronalelements. Adhesions can prevent the normal motions of tissues and organswith respect to their neighbouring structures. Adhesions are aparticular problem in gastrointestinal and gynaecological surgery,leading to post-operative bowel obstruction, infertility, and chronicpelvic pain.

The medical and scientific communities have studied ways of reducing theformation of post-surgical adhesions by the use of high molecular weightcarboxyl-containing biopolymers. These biopolymers can form hydratedgels which act as physical barriers to separate tissues from each otherduring healing, so that adhesions between normally adjacent structuresdo not form. After healing is substantially complete, the barrier is nolonger needed, and should be eliminated from the body to permit morenormal function of the affected tissues.

KR 2001 107 067 describes an adhesion preventing agent comprising 1.0-15wt % of alginate having a viscosity of 150 centipoise, 0-2.5 wt % ofpolyethylene glycol having a molecular weight of 3,000-5,000, 0-8 wt %of agarose, 0-1 wt. % of an antibiotic, and 73.5-99.0 wt % of water. Theadhesion preventing agent is sterilized at a temperature of less than150° C. for 5-20 minutes.

U.S. Pat. No. 6,150,581 (United States Surgical Corporation) describes amethod for preventing post surgical adhesions comprising:

-   -   providing an aqueous solution of chitosan and a complexing        agent;    -   providing an aqueous solution of alginate; and    -   combining the chitosan/complexing agent solution with the        alginate solution to form an anti-adhesion barrier at a site of        surgical intervention.

U.S. Pat. No. 6,638,917 (Boston Scientific SciMed, Inc) describe amethod of forming a sheet for use as an adhesion barrier, comprising:

-   -   forming a film from an alginate solution; and    -   contacting the film with a cross-linking solution to form a        cross-linked mechanically stable sheet for placement of at least        a portion of the sheet at a site of trauma to create the        adhesion barrier

WO 2006/044342 A2 (FMC Biopolymer AS) describes a method of using a selfgelling alginate dispersion to prevent post surgical adhesion formationin an individual, said method comprising dispensing a self gellingalginate dispersion within an individual by:

-   a) forming a dispersion by mixing i) a solution comprising a soluble    alginate with an insoluble alginate/gelling ion particles or ii)    immediately soluble alginate, insoluble alginate/gelling ion    particles and a solvent, and-   b) dispensing the dispersion whereby the dispersion forms an    alginate gel matrix.

The present invention aims to provide a sterile, ready-to-usealginate-based aqueous composition of neutral pH that has excellentstorage stability, that can be directly applied as such at the site oftrauma, and that is easy to manufacture. In particular, the presentinvention relates to a sterile alginate-based aqueous gel formulationthat can be produced using heat sterilization of the total compositionand that is heat stable as well as storage stable in terms of pH andrheological properties (e.g. viscosity).

SUMMARY OF THE INVENTION

The inventors have discovered that the aforementioned desirable featurescan be realized in an alginate-based aqueous composition that has beensterilized by heat sterilization and that contains 0.5-10 wt. % of analginate salt and 10-500 mM of one or more dissolved C₂-C₇ mono- ordicarboxylates that are optionally substituted with up to 2 hydroxylgroups, said alginate-based composition further being characterized by apH of 6.5-7.5 and a viscosity at 25° C. of at least 300 cP.

The specifications for alginate-based compositions have to be very tightgiven that these compositions are often applied in critically illpatients and furthermore, because they are applied directly at the siteof surgical trauma. However, meeting such tight specifications poses amajor challenge in case the composition is alginate-based.

It is known from e.g. Holme et al. 2008 (Kinetics and mechanisms ofdepolymerization of alginate and chitosan in aqueous solution.Carbohydrate Polymers 2008, Vol. 73, 656-664), Home et al. 2003 (Thermaldepolymerization of alginate in the solid state. Carbohydrate Polymers2003, Vol. 54, 431-438.) and Bradley et al. (The Determination ofKinetics of Polysaccharide Thermal Degradation using High TemperatureViscosity Measurements. Carbohydrate Polymers 1988, Vol. 9, 257-267)that both heat sterilization and storage induce decomposition ofalginate, resulting in time-dependent changes of pH and viscosity.

The inventors have also found that heat sterilization, especially moistheat sterilization above 100° C., tends to adversely effect both thepH-stability and rheological stability of alginate-based aqueouscompositions. Investigations undertaken by the inventors ultimatelyshowed that this particular instability was somehow linked to thebuffering systems (e.g. phosphate buffers) that are used to render thesecompositions biocompatible. In addition, the inventors have unexpectedlydiscovered that alginate-based aqueous compositions of neutral pHcontaining 0.01-0.5M of one or more dissolved C₂-C₇ mono- ordicarboxylates do not suffer from this instability and thatalginate-based compositions that are buffered by these carboxylates cansuitably be heat sterilized. Examples of C₂-C₇ mono- or dicarboxylatesthat may suitably be employed include acetate, propionate, fumarate,tartarate and benzoate.

U.S. Pat. No. 5,693,624 (Johnson & Johnson Medical Inc.) describes anaqueous gel composition for use as a wound dressing comprising from 2%to 10% w/v of a water-soluble alginate salt and from 1% to 40% w/v of aC₃-C₆ dihydric or trihydric alcohol, said composition beingsubstantially sterile and having been sterilized by heat sterilization.In the US patent it is stated that the inclusion of relatively largeamount of polyhydric alcohol (more than 15% w/v) results in an alginategel that is stabilised against hydrolysis and consequent loss ofviscosity during autoclave sterilization.

The present invention also provides a process for preparing analginate-based aqueous composition as described above, said processcomprising combining a water-soluble alginate salt; the one or moreC₂-C₇ mono- or dicarboxylates and water, followed by heat sterilization

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, one aspect of the invention relates to an aqueousalginate-based composition that has been sterilized by heatsterilization and having a viscosity at 25° C. of at least 300 cP(Helipath® T F spindle, 100 rpm), said composition having a pH in therange of 6.5-7.5; containing 0.5-10 wt. % of an alginate salt; andfurther containing 10-500 mM of one or more dissolved C₂-C₇ mono- ordicarboxylates that are optionally substituted with up to 2 hydroxylgroups.

Whenever reference is made in this document to a “C_(n),monocarboxylate”, what is meant is a monocarboxylate substance thatcontains n carbon atoms, including the carbon atom of the carboxylgroup. Likewise, the term “C_(n), dicarboxylate” refers to adicarboxylate substance that contains n carbon atoms, including the twocarbon atoms of the carboxyl groups. Thus, acetate is an example of a C₂monocarboxylate and succinate is an example of a C₄ dicarboxylate.

Although the inventors do not wish to be bound by theory, it is believedthat the C₂-C₇ mono- or dicarboxylates act as buffering agents. Here theterm “buffering agent” refers to substances that can be used in aqueoussystems to drive an acidic or basic solution to a certain pH (e.g. a pHwithin the range of 6.5-7.5) and that prevent a change in this pH.

Buffering agents can be either the weak acid or weak base that wouldcomprise a buffer solution (an aqueous solution comprising a mixture ofa weak acid and its conjugate base or a weak base and its conjugateacid). Buffering agents are the substances that are responsible for thebuffering seen in buffer solutions. Buffering agents are similar tobuffer solutions in that buffering agents are the main components ofbuffer solutions. They both regulate the pH of a solution and resistchanges in pH. A buffer solution maintains the pH for the whole systemwhich is placed into it, whereas a buffering agent can be added to analready acidic or basic solution, which it then modifies and maintains anew pH.

Typically, the alginate-based composition has a viscosity at 25° C. ofnot more than 10,000 cP. Preferably, said viscosity lies within therange of 500-8,000 cP, even more preferably of 700-4,000 cP. Thealginate-based composition advantageously has a sufficiently highviscosity to prevent it from flowing away from the trauma site and asufficiently low viscosity to allow it to spread out over the traumasite.

The altginate-based composition of the present invention offers theadvantage that it is ready-for-use and that it is a single componentsystem, as opposed to some of the two-component systems described in theprior art. The present composition can be a viscous liquid or a gel thatcan be rendered flowable by applying pressure or shear (e.g. athixotropic gel).

Alginates are hydrophilic biopolymers with the unique ability to formheat-stable gels that can develop and set at physiologically relevanttemperatures. Alginates are a family of non-branched binary copolymersof 1-4 glycosidically linked β-D-mannuronic acid (M) and α-L-guluronicacid (G) residues. The relative amount of the two uronic acid monomersand their sequential arrangement along the polymer chain vary widely,depending on the origin of the alginate. Alginate is the structuralpolymer in marine brown algae such as Laminaria hyperborea, Macro cystispyrifera, Lessonia nigrescens and Ascophyllum nodosum. Alginate is alsoproduced by certain bacteria such as Pseudomonas aeruginosa, Azotobactervinelandii and Pseudomonas fluoresceins (WO 04/011628).

The present invention utilizes an alginate salt, preferably an alginatemetal salt. Even more preferably, the alginate salt comprises one ormore cations selected from Na⁺, K⁺, Ca²⁺ and Mg²⁺.

The amount of alginate salt contained in the present alginate-basedcomposition preferably lies within the range of 1-5 wt. %. Mostpreferably, the alginate salt content of the composition is in the rangeof 1.2-4 wt. %.

Best results are obtained with the present alginate-based composition ifthe a high molecular weight alginate salt is employed. Accordingly, thealginate salt advantageously has a molecular weight of at least 50,000g/mol, even more preferably of at least 400,000 g/mol.

The present aqueous composition can advantageously be used as ananti-adhesion composition. Alternative medical applications include theuse as an implant or as an oral dosage unit. Especially in case of thelatter applications, the aqueous composition advantageously contains apharmaceutically active ingredient. It will be understood that for theaforementioned medical applications it is highly desirable to employ anultrapure alginate, i.e. an alginate from which endotoxins have beenremoved almost completely. Preferably, the alginate employed inaccordance with the present invention is an alginate that meets thestandard laid down in ASTM F2064-00 (reapproved 2006).

It is well-known that alginate gels can be produced when a multivalentcation (e.g. Ca²⁺) forms ionic bonds with the negatively charged groupfrom a G residue from two or more different alginate polymers, therebycross-linking these polymers. The formation of multiple cross-linkagesamong numerous alginate polymers results in the matrix that is thealginate gel structure.

According to a preferred embodiment at least a part of the alginatessalt contained in the alginate-based composition is cross-linked bydivalent cations selected from Ca²⁺, Mg²⁺ and combinations thereof.Advantageously, the alginate in the present composition is onlymoderately cross-linked in order to prevent the composition frombecoming a rigid gel. Typically, the total content of divalent cationsselected from Ca²⁺, Mg²⁺ and combinations thereof is within the range of10-3000 μmol per gram of alginate, more preferably 20-1200 μmol per gramof alginate per gram of alginate and most preferably 40-800 μmol pergram of alginate per gram of alginate. Moderate cross-linking of thealginate was found to reduce the pH drift observed during sterilisation.Furthermore, the inventors have observed that such cross-linkingimproves stability of pH and viscosity during storage.

The total content of monovalent cations selected from Na⁺, K⁺ andcombinations thereof preferably lies within the range of 0.5-50 mmol,more preferably 1-30 mmol and most preferably 2-20 mmol per gram ofalginate

The amount of the one or more C₇-C₇ mono- or dicarboxylates employed inthe present alginate-based composition preferably lies within the rangeof 15 to 400 mmol/l. Even more preferably, the amount of buffering agentis within the range of 20-300 mmol/l.

The C₂-C₇ mono- or dicarboxylates may be saturated or unsaturated,linear or cyclic. In accordance with a preferred embodiment of thepresent invention, the one or more mono- or dicarboxylates are saturatedor unsaturated, linear C₂-C₄ mono- or dicarboxylates that are optionallysubstituted with up to 2 hydroxyl groups. More preferably, the one ormore carboxylates are saturated, linear C₇-C₄ mono- or dicarboxylatesthat are substituted with up to 2 hydroxyl groups. Even more preferably,the one or more carboxylates are unsubstituted, saturated, linear C₂-C₄mono- or dicarboxylates, especially unsubstituted, saturated, linearC₂-C₄ monocarboxylates, e.g. acetate, propionate.

According to another advantageous embodiment, the C₂-C₇ mono- ordicarboxylates are aromatically unsaturated cyclic C₇ monocarboxylates,e.g. benzoate.

According to a particularly preferred embodiment of the presentinvention, the one or more C₂-C₇ mono- or dicarboxylates employed in thealginate-based composition are represented by the following formula:

wherein R represents R¹(R²)CH; R³—CH═CH or fenyl;

R¹ representing hydrogen or hydroxyl;

R² representing hydrogen or R⁴(R⁵)CH;

R³ representing methyl or COOH;

R⁴ representing hydrogen or hydroxyl; and

R⁵ representing hydrogen or COOH.

Examples of C₂-C₇ mono- or dicarboxylates encompassed by theaforementioned formula include: acetate, propionate, crotonate,succinate, fumarate, tartarate and benzoate.

In accordance with one advantageous embodiment of the invention thecarboxylate employed is represented by the aforementioned formulawherein R represents R¹(R²)CH. Examples of such mono- or dicarboxylatesinclude acetate, propionate succinate, and tartarate. More preferably,R¹ represents hydrogen and R² represents hydrogen, CH₃, CH₂COOH orCH(OH)COOH. According to a particularly preferred embodiment, the one ormore carboxylates are selected from acetate (R¹═H; R²═H) and propionate(R¹=H; R²=methyl). Most preferably, the carboxylate is acetate.

According to a particularly advantageous embodiment of the presentinvention, the alginate-based composition comprises acetate incombination with 0.1-5 mM of dissolved carbonate. The inventors havediscovered that the use of this particular combination of bufferingagents offers the advantage that the pH drop that is normally observedduring heat sterilization of the composition can be minimizedeffectively. In the alginate-based composition acetate and carbonate arepreferably employed in a molar ratio of 10:1 to 250:1, more preferablyin a molar ratio of 20:1 to 200:1.

In accordance with another advantageous embodiment the carboxylatecontained in the aqueous composition is benzoate. The inventors havefound that benzoate can be used produce an alginate-based compositionwhose pH remains remains virtually unchanged during sterilisation andsubsequent storage.

Yet another beneficial embodiment relates to an aqueous composition inwhich the mono- or dicarboxylates employed are represented by theaforementioned formula wherein R represents R³—CH═CH. The carboxylatesencompassed are fumarate and crotonate.

As explained herein before, the alginate-based composition of thepresent invention offers the important advantage that its pH remainsstable during storage, even when the product is stored at elevatedtemperatures. Accordingly, in accordance with another preferredembodiment, the pH of the composition remains within the range of6.5-7.5 when the composition is kept at 40° C. for 6 months.

In order to ensure that, for instance, atmospheric carbon dioxide willnot influence the pH of the alginate-based composition, said compositionis preferably packaged without a headspace or with a headspace thatcontains no carbon dioxide. Even more preferably, the headspace containsan inert gas such as nitrogen.

The alginate-based composition of the present invention is surprisinglystable under sterilization conditions, notably moist heat sterilizationat temperatures well above 100° C. This characteristic is evident fromthe fact that the composition can be heated to high temperature for asignificant amount of time without resulting in a substantial viscositydecrease and/or pH change. Thus, a preferred alginate-based compositionmeets the condition that its viscosity at 25° C. of the aqueouscomposition does not drop by more than 50% if the aqueous composition isheated to 121° C. for 15 minutes.

The bulk of the present alginate-based aqueous composition consists ofwater. Typically, the alginate-based composition contains 95-99 wt. % ofwater.

Besides the alginate salt, the one or more C₂-C₇ mono- or dicarboxylatesand the water, the alginate-based composition may suitably contain othercomponents, such a pharmaceutically active substances (e.g.antimicrobials, anti-inflammatories), dextran sulphate, dermatansulphate, pentosan polysulphate, sodium chloride etc.

To limit the alginate's tendency to promote the growth ofintra-abdominal anaerobic bacteria, possibly leading to intra-abdominalabcess formation or causing localized peritonitis to develop intogeneralized peritonitis, the alginate based composition advantageouslycontains a biocompatible anti-microbial agent, to inhibit growth ofintra-abdominal anaerobic bacteria.

The aqueous alginate-based composition of the present invention, unlikethe sterile wound dressing compositions described in U.S. Pat. No.5,693,624, preferably contains less than 15% (w/v) of polyhydricalcohol, e.g. a C3-C6 polyhydric alcohol such as propylene glycol orhexylene glycol. Even more preferably the alginate-based compositioncontains less than 10% (w/v), most preferably less than 1% (w/v)polyhydric alcohol.

Likewise, the alginate-based composition of the present invention,unlike the adhesion preventing agent taught by KR 2001 107 067 does notcontain polyethylene glycol having a molecular weight of 3,000-5,000.

The aqueous alginate-based composition preferably is more or lessisotonic. Thus, the alginate-based composition preferably contains C⁻ ina concentration of 20-300 mmol/l, more preferably in a concentration of50-250 mmol/l.

Another aspect of the invention relates to a process for preparing analginate-based aqueous composition as defined herein before, saidprocess comprising combining a water-soluble alginate salt; the one ormore C₂-C₇ mono- or dicarboxylates and water, followed by moist heatsterilisation.

Preferably, the sterilization conditions employed in the present processachieve a sterility assurance level of less than 10⁻⁵, more preferablyof less than 10⁻⁶.

In the present process heat sterilisation is suitably achieved byheating to a temperature of at least 100° C. for at least 5 minutes.Even more preferably, said heat sterilization involves heating to atemperature of at least 110° C. for at least 5 minutes, more preferablyfor at least 10 minutes. Most preferably, the heat sterilizationinvolves heating to a temperature of at least 115° C. for at least 5minutes, especially at least 10 minutes.

According to a particularly preferred embodiment, the moist heatsterilization employs high pressure steam. Even more preferably, themoist heat sterilization is carried out in an autoclave.

As explained herein before, preferably at least some of the alginatesalt is cross-linked by multivalent (metal) cations. Advantageously thiscross-linking is achieved by combining an aqueous solution of thealginate salt with an aqueous solution containing multivalent cations.More particularly, the present process advantageously comprisescombining an aqueous solution of 6-120 g/l of the water-soluble alginatesalt with an aqueous solution containing 3-250 mmol/l of divalentcations selected from Ca²⁺, Mg²⁺ and combinations thereof. According aparticularly preferred embodiment, the aqueous solution of thewater-soluble alginate salt and the aqueous solution of the divalentcations are combined in a weight ratio that lies within the range of 1:2to 10:1. Preferably, the one or more C₂-C₇ mono- or dicarboxylates arecontained in the aqueous solution of the water-soluble alginate salt.

The present invention offers the advantage that pH of the alginate-basedcomposition not only remains stable after heat sterilization, but alsothat the pH hardly changes during sterilization. Typically, the pHchange observed during sterilization is less than 1.0 pH-unit, morepreferably less than 0.5 pH-unit. Generally speaking, duringsterilization the pH of the alginate-based composition remains withinthe range of 6.5-7.5

The invention is further illustrated by means of the followingnon-limiting examples.

EXAMPLES Example 1

This Example demonstrates the influence of different buffering agents onthe pH and viscosity of heat sterilized alginate-based aqueouscompositions.

Alginate-based aqueous compositions (100 ml) were prepared on the basisof the following recipe:

Ingredient Amount Sodium alginate^(#) 2200 mg CaCl₂   1.6 mg Dextransulphate  53.8 mg NaCl  806 mg Buffering agent Specified below WaterRemainder (to 100 ml) ^(#)Manugel ® DMB, high G alginate (visc. 300 cP;1% aq. solution), ex FMC BioPolymer

The alginate-based aqueous compositions were compounded with thefollowing physiologically acceptable buffers to produce a bufferedcomposition having a pH of 7.50:

-   -   citrate (270 mg of sodium citrate)    -   phosphate (67 mg of NaH₂PO₄ and 220 mg of Na₂HPO₄)    -   acetate (270 mg of sodium acetate)    -   carbonate (270 mg of sodium bicarbonate)

In addition, a reference composition containing no buffering agent wasprepared. In all cases pH was adjusted to 7.5 with the help of 0.1N NaOHor 0.1N HCl.

Buffer compositions were made by accurately weighing the ingredientsinto the mixing flask and making up to volume with water for injection.Sodium chloride and dextran sulfate were then added to the buffersolution and dissolved. Ultrapure sodium alginate was then mixed intothe solution to afford a homogeneous clear gel. A second solutioncontaining the chosen buffer and calcium chloride was made after whichit was combined with the gel.

Subsequently, the alginate-based aqueous compositions were sterilized bysteam sterilisation (30 minutes at 121° C.). This sterilisation processis a worst case challenge. Normal sterilisation conditions to achieveSAL (sterility assurance level) of 10⁻⁴ is heating at 121° C. for 15minutes.

After sterilization, the viscosity of the different bufferedalginate-based aqueous compositions at 25° C. was determined at 100 rpm,using a Helipath® T F spindle. Also the viscosity of the referencecomposition was determined, both before and after sterilization.Likewise, the pH of the buffered compositions was measured aftersterilization and the pH of the reference composition was determinedbefore and after sterilization.

The data so obtained are depicted in the following table

Before sterilization After sterilization Buffering agent Viscosity pHViscosity pH Citrate 600 7.5 100 6.56 Phosphate 600 7.5 <50 6.05 Acetate600 7.5 250 6.37 Carbonate 600 7.5 125 8.66 Reference 600 7.5 500 5.74

These results show that the pH decrease observed during sterilizationcan be minimized by inclusion of a buffering agent. In addition, thedata shows that of the buffering systems tested, acetate showed thelowest viscosity decrease as a result of sterilization.

Example 2

Example 1 was repeated, but this time using the following bufferingagents in the indicated concentrations:

-   -   Propionic acid (0.1M)    -   Fumaric acid (0.05M)    -   Succinic acid (0.1M)    -   Crotonic acid (0.1M)    -   Sodiumhydrogen tartrate (0.1M)    -   Sulphuric acid (0.1M)    -   Ascorbic acid (0.1M)    -   Sodium benzoate (0.1M)    -   Boric acid (0.1M)    -   Monoethanol amine (0.1M)

It was found that pH stability of the compositions containing sulphuricacid or monoethanol amine was unacceptable. Furthermore, thecompositions containing boric acid, ascorbic acid or monoethanol aminewere found to suffer from unacceptable viscosity fluctuations duringheat sterilisation. The pH- and viscosity stability of the otheralginate-based compositions was acceptable. Of these compositions, thealginate-based compositions containing sodium benzoate, crotonate orsuccinate performed best.

Example 3

An alginate-based buffered aqueous composition (100 ml) was prepared onthe basis of the following recipe, using the methodology described inexample 1 (under an inert atmosphere of N₂ to avoid absorption of CO₂from ambient air). This time, however, the pH of the aqueouscompositions was set to 7.0 prior to sterilization

Ingredient Amount Sodium alginate 2000 mg  Dextran sulphate 53.8 mg NaCl 800 mg Sodium acetate 500 mg Sodium bicarbonate 0-50 mg  WaterRemainder (to 100 ml)

To investigate long-term stability as well as the robustness of the pHstabilization, the pH was determined after 30 and 60 minutes ofsterilization. Four formulations containing different amounts ofcarbonate were subjected to the identical sterilization conditions (seeExample 1). The results obtained are depicted in the following table.

Amount of sodium pH after 30 minutes pH after 60 minutes Specificationbicarbonate sterilization sterilization 6.5-7.5  0 mg 6.8 6.0 Out ofspec  9 mg 7.2 7.1 Within spec 36 mg 7.7 7.5 Within spec 50 mg 8.0 7.8Out of spec

These results show that the formulation with the lowest carbonateaddition (9 mg) yields the most stable pH profile. Even after a steamsterilization cycle of 60 minutes, the pH stays within a pH range of6.5-7.5.

Example 4

The formulation described in Example 3 containing 500 mg of sodiumacetate and 9 mg of sodium bicarbonate was used in a series ofexperiments designed to test the influence of CaCl₂ cross-linking on pHstability and viscosity. The influence of different concentrations ofCaCl₂ on pH immediately after sterilization is depicted in the followingtable.

pH increase after 30 Amount of CaCl₂ minutes sterilization  0 mg 0.27 33mg 0.22 66 mg 0.23 99 mg 0.37

In addition, the stability of these formulations during storage wastested. The samples were put in thermostatic ovens at differenttemperatures. pH was measured at regular intervals over a period of 3months. The results are represented in the following tables.

pH pre- 0 4 8 12 specification CaCl₂ Temperature sterilization weeksweeks weeks weeks 6.5-7.5 99 mg  4° C. 6.9 7.5 7.2 7.0 7.0 within spec25° C. 7.1 7.4 7.4 7.1 7.0 within spec 40° C. 6.9 7.3 7.1 7.2 6.9 withinspec 60° C. 7.0 7.3 7.0 7.7 8.0 out of spec 66 mg  4° C. 6.8 7.0 7.2 7.07.2 within spec 25° C. 6.9 7.7 7.2 6.9 7.2 within spec 40° C. 7.0 7.37.2 7.2 6.9 within spec 60° C. 7.0 7.7 8.7 8.1 6.9 out of spec 33 mg  4°C. 6.9 7.1 7.1 6.9 7.1 within spec 25° C. 6.9 7.2 6.9 6.8 6.9 withinspec 40° C. 7.0 7.2 7.2 7.0 7.1 within spec 60° C. 6.9 7.0 7.1 7.0 7.6out of spec  0 mg 60° C. 6.9 7.2 7.8 8.5 7.6 out of spec

Furthermore, for the viscosity of the formulations was monitored over athree month storage period (at 60° C.), yielding the following results:

Viscosity in cP CaCl₂ 0 weeks 4 weeks 8 weeks 12 weeks 99 mg 5000 23001800 1400 66 mg 3850 1830 1990 1010 33 mg 1500 800 650 750  0 mg 1950550 450 500

These results show that moderate cross linking with calcium ions (33 mgor 66 mg CaCl₂) gives increased pH stability and improved viscositystability.

Example 5

In order to investigate the possible influence of alginate molecularweight (Mw) characterised by viscosity on pH stability, two alginatesalts having different molecular weight distributions were tested, onehigh molecular weight alginate (Manugel DMB, FMC Biopolymer, viscosity300 cP 1% solution) and one low molecular weight alginate (Manugel LBA,FMC Biopolymer, viscosity 700 cP 10% solution). Formulations wereprepared using the methodology described in example 1 and subjected tosterilization times of 0 to 100 minutes. The pH of the formulations wasmonitored during sterilization. The results obtained showed that the pHof the formulation containing the high molecular weight alginate variedby no more than 0.3 pH units from the initial pH. The formulationcontaining the low molecular weight alginate showed a pH drift of 0.7 pHunits.

Example 6

Anti-adhesion compositions for surgical use should be physiologicallyacceptable and hence preferably should not be hyper or hypo-osmotic. Ananti-adhesion composition having an osmolality of 280-295 mOsm/l wasprepared on the basis of the following recipe, using the methodologydescribed in Example 1.

Ingredient mg/ml (anhydrous) Polydextran sulphate 0.525 Alginate 20 NaCl4.6 NaCO₂CH₃ 5 NaHCO₃ 0.0833 CaCl₂ 0.33

This composition was prepared under GMP conditions in three independentproduction runs (three batches), filled into 100 mL syringes andsterilised at 121° C. for 15 minutes. After sterilisation, of eachbatch, an adequate amount of syringes was tested on pH, viscosity,osmolality, assay sodium alginate, assay polydextran sulphate, assay ofcalcium, endotoxins and sterility. All parameters were within presetspecifications. The three batches were then stored to perform astability study, according to ICH Guidance, at 25° C., 60% relativehumidity and tested on pH and viscosity (visc.) after 0 (initial), 3, 6,12 and 18 months storage. The results were as follows:

Shelf life specifications Initial 3 months 6 months 12 months 18 monthspH Batch-1 6.5-7.5 6.9 6.8 6.9 7.1 7.1 Batch-2 6.5-7.5 7.0 7.0 6.9 7.17.0 Batch-3 6.5-7.5 6.9 6.9 7.0 7.1 7.0 Visc. Batch-1   1000-10.000 31002843 3010 3050 3010 (mPa · s) Batch-2   1000-10.000 3718 3815 3566 36843899 (mPa · s) Batch-3   1000-10.000 2950 2915 3010 3025 3000 (mPa · s)

1.-15. (canceled)
 16. A sterile aqueous composition having a viscosityat 25° C. of at least 300 cP (Helipath® T F spindle, 100 rpm at 25° C.)and a pH in the range of 6.5-7.5, the composition comprising 0.5-10 wt.% of an alginate salt and 10-500 mM of one or more dissolved C₂-C₇ mono-or dicarboxylates that are optionally substituted with up to 2 hydroxylgroups.
 17. The aqueous composition according to claim 16, having aviscosity at 25° C. of less than 10,000 cP.
 18. The aqueous compositionaccording to claim 17, having a viscosity at 25° C. of 500-8,000 cP. 19.The aqueous composition according to claim 16, comprising 1-5 wt. % ofthe alginate salt.
 20. The aqueous composition according to claim 16,wherein the alginate salt has a molecular weight of at least 50,000g/mol.
 21. The aqueous composition according to claim 20, wherein thealginate salt has a molecular weight of at least 400,000 g/mol.
 22. Theaqueous composition according to claim 16, wherein the alginate salt iscross-linked by divalent cations selected from Ca²⁺, Mg²⁺ andcombinations thereof.
 23. The aqueous composition according to claim 16,wherein the total content of divalent cations selected from Ca²⁺, Mg²⁺and combinations thereof is within the range of 10-3000 μmol per gram ofalginate.
 24. The aqueous composition according to claim 23, wherein thetotal content of divalent cations selected from Ca²% Mg²⁺ andcombinations thereof is within the range of 20-1200 μmol per gram ofalginate.
 25. The aqueous composition according to claim 16, wherein theone or more C₂-C₇ mono- or dicarboxylates are saturated or unsaturated,linear C₂-C₄ mono- or dicarboxylates that are optionally substitutedwith up to 2 hydroxyl groups.
 26. The aqueous composition according toclaim 16, wherein the one or more C₂-C₇ mono- or dicarboxylates arerepresented by the following formula:

wherein R represents R¹(R²)CH: R³—CH═CH or fenyl; R¹ representinghydrogen or hydroxyl; R² representing hydrogen or R⁴(R⁵)CH; R³representing methyl or COON; R⁴ representing hydrogen or hydroxyl; andR⁵ representing hydrogen or COOH.
 27. The aqueous composition accordingto claim 26, wherein R represents R¹(R²)CH.
 28. The aqueous compositionaccording to claim 26, wherein R¹ represents hydrogen; and R² representshydrogen, CH₃, CH₂COOH or CH(OH)COOH.
 29. The aqueous compositionaccording to claim 26, wherein R represents fenyl.
 30. The aqueouscomposition according to claim 26, wherein R represents R³—CH═CH.
 31. Aprocess for preparing an aqueous composition according to claim 16,comprising (a) combining a water-soluble alginate salt; the one or moreC₂-C₇ mono- or dicarboxylates and water, and (b) sterilizing thecomposition.
 32. The process according to claim 31, comprising combiningan aqueous solution of 6-120 g/l of the water-soluble alginate salt withan aqueous solution containing 3-250 mmol/l of divalent cations selectedfrom Ca²⁺, Mg²⁺ and combinations thereof.
 33. The process according toclaim 32, wherein the aqueous solution of the water-soluble alginatesalt and the aqueous solution of the divalent cations are combined in aweight ration between 1:2 to 10:1.